Method ThreadDNSAddressSeed

src/net.cpp:1736–1845

}

void CConnman::ThreadDNSAddressSeed()
{
    SetSyscallSandboxPolicy(SyscallSandboxPolicy::INITIALIZATION_DNS_SEED);
    FastRandomContext rng;
    std::vector<std::string> seeds = Params().DNSSeeds();
    Shuffle(seeds.begin(), seeds.end(), rng);
    int seeds_right_now = 0; // Number of seeds left before testing if we have enough connections
    int found = 0;

    if (gArgs.GetBoolArg("-forcednsseed", DEFAULT_FORCEDNSSEED)) {
        // When -forcednsseed is provided, query all.
        seeds_right_now = seeds.size();
    } else if (addrman.size() == 0) {
        // If we have no known peers, query all.
        // This will occur on the first run, or if peers.dat has been
        // deleted.
        seeds_right_now = seeds.size();
    }

    // goal: only query DNS seed if address need is acute
    // * If we have a reasonable number of peers in addrman, spend
    //   some time trying them first. This improves user privacy by
    //   creating fewer identifying DNS requests, reduces trust by
    //   giving seeds less influence on the network topology, and
    //   reduces traffic to the seeds.
    // * When querying DNS seeds query a few at once, this ensures
    //   that we don't give DNS seeds the ability to eclipse nodes
    //   that query them.
    // * If we continue having problems, eventually query all the
    //   DNS seeds, and if that fails too, also try the fixed seeds.
    //   (done in ThreadOpenConnections)
    const std::chrono::seconds seeds_wait_time = (addrman.size() >= DNSSEEDS_DELAY_PEER_THRESHOLD ? DNSSEEDS_DELAY_MANY_PEERS : DNSSEEDS_DELAY_FEW_PEERS);

    for (const std::string& seed : seeds) {
        if (seeds_right_now == 0) {
            seeds_right_now += DNSSEEDS_TO_QUERY_AT_ONCE;

            if (addrman.size() > 0) {
                LogPrintf("Waiting %d seconds before querying DNS seeds.\n", seeds_wait_time.count());
                std::chrono::seconds to_wait = seeds_wait_time;
                while (to_wait.count() > 0) {
                    // if sleeping for the MANY_PEERS interval, wake up
                    // early to see if we have enough peers and can stop
                    // this thread entirely freeing up its resources
                    std::chrono::seconds w = std::min(DNSSEEDS_DELAY_FEW_PEERS, to_wait);
                    if (!interruptNet.sleep_for(w)) return;
                    to_wait -= w;

                    int nRelevant = 0;
                    {
                        LOCK(m_nodes_mutex);
                        for (const CNode* pnode : m_nodes) {
                            if (pnode->fSuccessfullyConnected && pnode->IsFullOutboundConn()) ++nRelevant;
                        }
                    }
                    if (nRelevant >= 2) {
                        if (found > 0) {
                            LogPrintf("%d addresses found from DNS seeds\n", found);